1. Field of the Invention
The present invention relates to a tiller which is operable with a variable driving force and under variable tilling conditions, depending on the soil.
2. Description of the Related Art
A small tiller as disclosed in, for example, Japanese Utility Model Laid-Open Publication No. SHO-57-86502 is known as a controlled machine having tilling claws attached to a tilling shaft rotatably for cultivating the soil with the forward movement of the machine, as well as allowing it to run on a road. The machine has a plurality of appropriately spaced apart tilling claws attached to the tilling shaft extending transversely under its main body, a rearwardly extending operating handlebar, and a resistance bar extending rearwardly and downwardly from its main body.
As the tilling claws serve also as traveling wheels, however, the machine requires a great deal of labor and skill for its operation, since the nature of the soil may disable it to keep a good balance between its driving force and tillage, and call for a change of the tilling conditions. If the soil is hard, the machine suffers from a serious lowering of its operability due to a dashing phenomenon, since the tilling claws do not cut into the ground, but roll thereon and cause the machine to move forward uselessly. If the soil is soft, the machine has a lower working efficiency, as it is likely to work on the soil to an unnecessary extent and have a lower driving force.
A small tiller as disclosed in, for example, Japanese Utility Model Laid-Open Publication No. HEI-6-3002 is known as having been devised to solve those problems. The tiller has a connecting shaft connected to a tilling shaft, which is the output shaft of a transmission, and carrying tilling claws on its portion close to the transmission. The connecting shaft also carries thereon a planetary gear mechanism composed of a sun gear formed on its middle portion, a plurality of planet gears meshing with the sun gear and gear shafts each attached rotatably to the center of one of the planet gears. Traveling wheels are attached to the gear shafts of the planetary gear mechanism by bosses. A ring gear is rotatably fitted to the connecting shaft. The ring gear has a toothed inner periphery meshing with the planet gears. The ring gear is secured to a fender fixed to the transmission. The rotation of the tilling shaft is transmitted to the traveling wheels by the planetary gear mechanism, so that the traveling wheels may be rotated at a reduced speed relative to the tilling claws rotating with the tilling shaft. As the wheels have a fixed reduction ratio relative to the tilling shaft, however, the wheels have a fixed driving force for moving the machine forward, and under certain soil conditions, therefore, it is impossible to obtain the desired driving force for achieving any adequate tilling work. The tiller is so designed that a part of the planetary gear mechanism may be altered in structure to reverse the rotation of the traveling wheels relative to the tilling claws, but its structural alteration is a large-scaled and complicated job.
It is, therefore, an object of this invention to provide a tiller which can always maintain stability in operation to achieve an improved finish of tilling, a reduction of dashing and an improved ability to move forward irrespective of the conditions of the soil.
According to an aspect of this invention, there is provided a tiller for cultivating the soil, having a power source, a tilling shaft rotatable by a driving force supplied to it from the power source through a power transmission, and a plurality of tilling claws carried on the tilling shaft, the tilling shaft being a concentric dual-shaft structure having a hollow outer shaft and an inner shaft extending through the outer shaft, the inner shaft having its rotating speed and/or its direction of rotation variable relative to the outer shaft.
If the rotating speed of the inner shaft or its direction of rotation is altered relative to the outer shaft, it is easily possible to alter the tilling conditions as required to suit the nature of the soil of a field and thereby obtain the desired tillage and tilling speed, so that the tiller of this invention can maintain stability in operation despite any change in the nature of the soil. The alteration of the rotating speed of the inner shaft is particularly useful, as it makes it possible to select any tillage and tilling speed from a finely divided range to thereby obtain the soil which is suitable for growing any of various kinds of crops.
The power transmission may be composed of a first power transmission system for transmitting a driving force from the power source to the outer shaft and a second power transmission system for transmitting a driving force from the power source to the inner shaft, the second power transmission system including a hydrostatic transmission composed of a hydraulic pump and a hydraulic motor, as will be described more specifically. The hydrostatic transmission makes it possible to change the rotating speed of the inner shaft in a stepless way and control its direction of rotation selectively as desired.
In a preferred form, the outer and inner shafts are fitted with a plurality of tilling claws. The tiller can easily be moved backward on the ground if the inner shaft is rotated at an increased speed in the opposite direction to the outer shaft. The dashing of the tiller can be prevented during the tilling of hard soil by the rotation of the outer and inner shafts in the same direction if the inner shaft is rotated at a lower speed than the outer shaft, since the force for driving the tiller by the tilling claws fitted on the outer shaft is restrained by the claws on the inner shaft.
A side disk is fitted on each of the opposite ends of the inner shaft, and a plurality of tilling claws are fitted on the outer shaft. Each side disk is provided on its inner surface with a plurality of upstanding plates each lying at an angle to the radius of the disk for producing a greater amount of friction with the soil. The friction force produced in the soil by the upstanding plates on the side disks enables the tiller to remain stable on both sides throughout its operation to thereby achieve an improved straight drive. If the rotating speed of the side disks on the inner shaft or their direction of rotation is altered relative to the tilling claws on the outer shaft, it is possible to vary the driving force of the side disks as desired, so that the tilling conditions can easily be altered to suit the nature of the soil to realize any desired tillage and tilling speed. The alteration of the rotating speed of the side disks is particularly useful, since it makes it possible to select any tilling speed from a finely divided range and thereby control tillage as desired. Thus, this invention makes it possible to realize an adequate tilling speed for achieving an improved operating efficiency and the desired control of tillage for making the soil suitable for growing any of various kinds of crops.